Talk of Iran's nuclear program--and a potential military strike against it--dominated Republican presidential candidate Mitt Romney's brief diplomatic visit to Israel on Sunday, though Israeli politicians placed different emphases on the role of a military threat.

Prime Minister Binyamin Netanyahu Sunday told Romney in a Jerusalem meeting that diplomacy and sanctions leveled against Iran have not worked so far.

"I heard some of your remarks and you said that the greatest danger facing the world is the Ayatollah regime possessing nuclear weapons capability," Netanyahu said. "Mitt, I couldn't agree with you more, and I think it is important to do everything in our power to prevent the ayatollahs from possessing that capability. We have to be honest and say that all the diplomacy and sanctions and diplomacy so far have not set back the Iranian program by one iota."

Netanyahu said that a "strong and credible military threat coupled with sanctions" was needed to "have a chance to change the situation."

Romney said he wanted to hear Netanyahu's perspective regarding Iran and about "further actions that we can take to dissuade Iran from their nuclear folly."

Romney also said he was "honored" to be here on Tisha Be'Av, "to recognize the solemnity of the day and also the suffering of the Jewish people over the centuries and the millennia, and come with recognition of the sacrifices of so many. Unfortunately, the tragedies of wanton killing are not only things of the past, but have darkened our skies in even more recent times."

Following his meeting with Netanyahu, Romney met with President Shimon Peres.

Peres told Romney that Iran is bent on dominating the Middle East, and that he appreciates US efforts to block it by all means.

Iran, Peres said, spreads terror, finances terror, is developing a nuclear weapon "against the wishes of the entire world" and has threatened "to bring an end to Israel."

Praising the US policy of enacting diplomatic measures against the Islamic Republic, Peres emphasized that a military threat was necessary as well "in order to make it serious."

"We trust [the US position] includes a very serious and warm consideration of the security of Israel," Peres added. "It's far from being just an Israeli problem."

Opposition Leader Shaul Mofaz told Romney that non-military options on Iran have not yet run their course, but emphasized that "cooperation between Israel and the United States is more important than ever."

"We have to be ready for all options on Iran, but the time for military operations has not yet come," Mofaz told Romney. "This is a time to tighten the sanctions on the Iranian regime and be ready for any development which we should handle in full coordination."

In an implicit compliment to US President Barack Obama, Mofaz said that the American administration was committed on the issue.

The two also spoke about the need for Israel to mend ties with Turkey, and the importance of returning to the negotiating table with the Palestinians.

Romney canceled his planned meeting with Labor party head Shelly Yechimovich on Sunday.

Labor MK Isaac Herzog, who was meant to participate in the meeting as well, expressed regret at the meetings "surprising last-minute cancellation," saying he suspected the decision was politically motivated.

Earlier, a senior Romney aide said the former Massachusetts governor would back Israel if it were to decide it had to use military force to stop Iran from developing a nuclear weapon.

"If Israel has to take action on its own, in order to stop Iran from developing that capability, the governor would respect that decision," Romney's senior national security aide Dan Senor told reporters traveling with the candidate.

The comment made ahead of Romney meetings seemed to differ with US President Barack Obama's attempts to convince Israel to avoid any preemptive attack.

Senor told reporters that Romney believed the threat from Iran was approaching on a path involving two timelines.

The first was Iran's drive - denied by Tehran - to develop a nuclear weapons capability, and the second was having the ability to penetrate Iran's defenses before they were hardened in such a way to protect against a strike, Senor said.

In excerpts of a speech Romney was to deliver on Monday evening, the former Massachusetts governor planned to say that an aggressive approach to Tehran was needed to protect against a threat to the very existence of Israel, the closest US ally in the turbulent Middle East.

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"When Iran's leaders deny the Holocaust or speak of wiping this nation off the map, only the naïve - or worse - will dismiss it as an excess of rhetoric," he would say.

"Make no mistake: The ayatollahs in Tehran are testing our moral defenses. They want to know who will object, and who will look the other way."

Romney and Netanyahu will meet again later in the day after the Tisha Be’av fast when he and his wife, Ann, will dine at the Prime Minister’s Residence with Netanyahu and his wife, Sara.

Romney’s visit to Israel – his fourth – is widely considered an effort to woo pro-Israel voters in the US, both Jews and Evangelical Christians, many of whom are discontent with the Middle East policies of President Barack Obama.

Romney is slated to leave for Poland at about noon on Monday.

Before taking off, he is scheduled to host a fund-raiser at the King David Hotel in Jerusalem Monday morning. The event was moved from Sunday evening to Monday morning so as not to conflict with Tisha Be’av. The cost to attend the event, where Romney is expected to appear for 45 minutes, is $50,000 a couple.

Reuters contributed to this report.

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